1. Field of the Invention
The present invention relates to an embroidery machine, and more particularly to an apparatus which accurately controls the position of an embroidery frame in an embroidery machine by sensing a displacement of the embroidery frame and feeding back an error of the sensed movement of the embroidery frame and a method thereof.
2. Description of the Prior Art
As generally known in the art, an embroidery machine embroiders an embroidery design on a fabric fixed on an embroidery frame while a needle holder contained in a sewing device moves up and down, and simultaneously, the embroidery frame moves in directions along an X-axis and a Y-axis. Because the embroidery machine embroiders the embroidery design on the fabric while the embroidery frame moves as above the X-axis and the Y-axis, accurate movement and low vibration of the embroidery frame are closely related to the quality of embroidery.
Conventionally, the embroidery machine includes an alternating current (AC) servo-motor or an induction motor for moving the needle holder up and down. Alternatively, the embroidery machine includes a stepping motor for moving the embroidery frame along the X-axis and the Y-axis.
FIG. 1 is a block diagram showing a configuration of a conventional apparatus for controlling a position of an embroidery frame in an embroidery machine. The conventional apparatus for controlling a position of an embroidery frame includes a controller 10, an X-axis driver 20, and a Y-axis driver 30.
When an external embroidery frame displacement command signal is inputted to a controller 10, the controller 10 outputs X-axis and Y-axis drive control signals corresponding to the external embroidery frame displacement command signal. The external embroidery frame displacement command signal is a signal which requests the embroidery frame 400 to move along an X-axis direction and a Y-axis direction over predetermined displacements, respectively. The X-axis driver 20 includes an X-axis servo-motor (not shown) as a driving source to move the embroidery frame 40 to the X-axis direction. The X-axis driver 20 drives the X-axis servo-motor according to the X-axis drive control signal from the controller 10. The X-axis driver 20 moves the embroidery frame 40 along an X-axis direction by means of the driven X-axis motor by a predetermined displacement. The Y-axis driver 30 includes a Y-axis servo-motor (not shown as a driving source to move the embroidery frame 40 along the Y-axis direction. The Y-axis driver 30 drives the Y-axis servo-motor according to the Y-axis drive control signal from the controller 10. The Y-axis driver 30 moves the embroidery frame 40 along a y-axis direction by means of the driven Y-axis motor by a predetermined displacement.
X-axis and Y-axis servo motors of the X-axis and Y-axis drivers 20 and 30 transmit power to interlocking devices. The interlocking devices include a driving timing pulley, a driven timing pulley, and a shaft. During transferring the powers to the interlocking devices, an error occurs due to mutual operations of the interlocking devices. The error prevents the controller 10 from accurately controlling the position of the embroidery frame 40, causing a lowering of the quality of embroidery.
In order to solve the above problems, a power transmission method using a linear motor instead of the timing belt has been suggested. However, the power transmission method should have a plurality of linear motors and drivers for controlling a plurality of linear motors. This increases the manufacturing cost. Furthermore, since a plurality of linear motors should move the embroidery frame 20 in the same direction, there is a technical difficulty of synchronizing them.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide an apparatus for controlling a position of an embroidery frame, which is capable of performing an accurate embroidering operation by feeding back a position error due to mutual operations of interlocking devices for driving the embroidery frame using a displacement sensor for sensing a displacement of the embroidery frame, and a method thereof.
In order to accomplish this object, there is provided an apparatus for controlling a position of an embroidery frame in an embroidery machine, the embroidery machine having the embroidery frame for fixing a fabric, the apparatus comprising: a X-axis driver for moving the embroidery frame along an X-axis direction; a Y-axis driver for moving the embroidery frame along a Y-axis direction; a sensor for sensing a displacement of the embroidery frame along the X-axis and Y-axis directions, and outputting electric signals corresponding to the sensed displacement of the embroidery frame; and a controller for generating X-axis and Y-axis drive control signals based on the electric signals from the sensor in order to control the X-axis and Y-axis drivers, respectively.
Preferably, the controller includes a position detector for detecting the displacement of the embroidery frame based on the electric signals from the sensor; a speed detector for detecting a transport speed of the embroidery frame based on the displacement of the embroidery frame sensed by the sensor; and a current detector for detecting the first and second motor drive current signals provided from the X-axis and Y-axis drivers, wherein the controller generates the X-axis and Y-axis drive control signals using the displacement of the embroidery frame detected by the position detector, the transport speed of the embroidery frame detected by the speed detector, and the motor drive current signals detected by the current detector.
Preferably, the position detector includes a counter for counting the pulse number of the electric signals from the sensor, and the position detector detects the displacement of the embroidery frame along the X-axis and Y-axis directions based on the pulse number of the electric signal counted by the counter, and the speed detector detects the transport speed of the embroidery frame based on the number of the electric signal counted by the counter.
Preferably, the controller includes a first calculator for calculating a position error based on the displacement of the embroidery frame detected by the position detector and the displacement by an external embroidery frame displacement command signal; a position controller for generating a speed control signal based on the position error calculated by the first calculator; a second calculator for calculating a speed error based on the speed control signal from the position controller and the transport speed of the embroidery frame detected by the speed detector; a speed controller for generating a current control signal based on the speed error calculated by the second calculator; a third calculator for calculating an error of a driving current based on the current control signal generated by the speed controller and the current signal detected by the current detector; and a current controller for generating a drive control signal based on the error of a driving current calculated by the third calculator.
Also, the sensor is installed at a predetermined X-axis position of the embroidery frame. Further, the sensor is installed at a predetermined Y-axis position of the embroidery frame. The sensor comprises a displacement sensor. The displacement sensor outputs an electric signal which corresponds to the displacement sensed by the sensor in a linear scale fashion.
There is also provided a method for controlling a position of an embroidery frame which moves the position of the embroidery frame along X-axis and Y-axis directions according to X-axis and Y-axis drive control signals from the X-axis and Y axis drivers, the method comprising the steps of: (i) detecting an electric signal corresponding to a displacement after moving the embroidery frame along an X-axis and a Y-axis; and (ii) generating the X-axis and Y-axis drive control signals based on the electric signal detected in step (i).
Preferably, step (ii) includes the steps of: (ii-1) detecting the displacement of the embroidery frame based on the electric signal detected in step (i); (ii-2) detecting a transfer speed of the embroidery frame based on the displacement of the embroidery frame detected in step (ii-1); (ii-3) detecting motor drive current signals which the X-axis and Y-axis drivers output; and (ii-4) generating the X-axis and Y-axis drive control signals using the displacement of the embroidery frame detected in step (ii-1), the transfer speed of the embroidery frame detected in step (ii-2), and the motor drive current signals detected in step (ii-3).
Preferably, step (ii-1) includes the step of counting the pulse number of the detected electric signal, and the method detects a displacement and a transfer speed of the embroidery frame to the X-axis and Y-axis directions based on the pulse number.
Preferably, step (ii-4) includes the steps of: (ii-4-1) calculating a position error based on the displacement of the embroidery frame detected in step (ii-1) and an embroidery frame displacement command signal from the external; (ii-4-2) generating a speed control signal based on the position error calculated in step (ii-4-1); (ii-4-3) calculating a speed error based on the speed control signal generated in step (ii-4-2) and the transport speed of the embroidery frame detected in step (ii-2); (ii-4-4) generating a current control signal based on the speed error calculated in step (ii-4-3); (ii-4-5) calculating an error of a driving current based on the current control signal generated in step (ii-4-4) and the motor drive current signals detected in step (ii-3); and (ii-4-6) generating a drive control signal based on the error of a driving current calculated in step (ii-4-5). Also, step (ii-1) is performed in a linear scale fashion.